[PATCH 04/12] btrfs: remove remapped block groups from the free-space tree

[Mark Harmstone <maharmstone@fb.com>]

No new allocations can be done from block groups that have the REMAPPED flag
set, so there's no value in their having entries in the free-space tree.

Prevent a search through the free-space tree being scheduled for such a
block group, and prevent discard being run for a fully-remapped block
group.

Signed-off-by: Mark Harmstone <maharmstone@fb.com>
---
 fs/btrfs/block-group.c | 21 ++++++++++++++++-----
 fs/btrfs/discard.c     |  9 +++++++++
 2 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c
index 5b0cb04b2b93..9b3b5358f1ba 100644
--- a/fs/btrfs/block-group.c
+++ b/fs/btrfs/block-group.c
@@ -920,6 +920,13 @@ int btrfs_cache_block_group(struct btrfs_block_group *cache, bool wait)
 	if (btrfs_is_zoned(fs_info))
 		return 0;
 
+	/*
+	 * No allocations can be done from remapped block groups, so they have
+	 * no entries in the free-space tree.
+	 */
+	if (cache->flags & BTRFS_BLOCK_GROUP_REMAPPED)
+		return 0;
+
 	caching_ctl = kzalloc(sizeof(*caching_ctl), GFP_NOFS);
 	if (!caching_ctl)
 		return -ENOMEM;
@@ -1235,9 +1242,11 @@ int btrfs_remove_block_group(struct btrfs_trans_handle *trans,
 	 * another task to attempt to create another block group with the same
 	 * item key (and failing with -EEXIST and a transaction abort).
 	 */
-	ret = remove_block_group_free_space(trans, block_group);
-	if (ret)
-		goto out;
+	if (!(block_group->flags & BTRFS_BLOCK_GROUP_REMAPPED)) {
+		ret = remove_block_group_free_space(trans, block_group);
+		if (ret)
+			goto out;
+	}
 
 	ret = remove_block_group_item(trans, path, block_group);
 	if (ret < 0)
@@ -2457,10 +2466,12 @@ static int read_one_block_group(struct btrfs_fs_info *info,
 	if (btrfs_chunk_writeable(info, cache->start)) {
 		if (cache->used == 0) {
 			ASSERT(list_empty(&cache->bg_list));
-			if (btrfs_test_opt(info, DISCARD_ASYNC))
+			if (btrfs_test_opt(info, DISCARD_ASYNC) &&
+			    !(cache->flags && BTRFS_BLOCK_GROUP_REMAPPED)) {
 				btrfs_discard_queue_work(&info->discard_ctl, cache);
-			else
+			} else {
 				btrfs_mark_bg_unused(cache);
+			}
 		}
 	} else {
 		inc_block_group_ro(cache, 1);
diff --git a/fs/btrfs/discard.c b/fs/btrfs/discard.c
index 89fe85778115..1015a4d37fb2 100644
--- a/fs/btrfs/discard.c
+++ b/fs/btrfs/discard.c
@@ -698,6 +698,15 @@ void btrfs_discard_punt_unused_bgs_list(struct btrfs_fs_info *fs_info)
 	/* We enabled async discard, so punt all to the queue */
 	list_for_each_entry_safe(block_group, next, &fs_info->unused_bgs,
 				 bg_list) {
+		/* Fully remapped BGs have nothing to discard */
+		spin_lock(&block_group->lock);
+		if (block_group->flags & BTRFS_BLOCK_GROUP_REMAPPED &&
+		    !btrfs_is_block_group_used(block_group)) {
+			spin_unlock(&block_group->lock);
+			continue;
+		}
+		spin_unlock(&block_group->lock);
+
 		list_del_init(&block_group->bg_list);
 		btrfs_discard_queue_work(&fs_info->discard_ctl, block_group);
 		/*
-- 
2.49.0